The present application claims priority upon Japanese Patent Application No. 2001-288833 filed on Sep. 21, 2001, which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a data processing system comprising a host processing device and a storage control device connected to the host processing device via a communication means and storing data sent from the host processing device, and the storage control device using this data processing system. In particular, the present invention relates to a technique for assigning an alias device to a base device in order to maximize the effect of the alias device from a viewpoint of the entire processing of the data processing system, in a mechanism where, in case the host processing device conducts an I/O process to a certain logic device (hereinafter referred to as “base device”) and a control block assigned to the logic device (hereinafter referred to as “base control block”) is in use thereupon, the process is conducted by a control block (hereinafter referred to as “alias control block”) assigned to another logic device (hereinafter referred to as “alias control block”).
2. Description of the Related Art
In a data processing system constructed by connecting a host processing device, such as a main frame, and a storage control device, such as a disk array device, when an I/O request is conducted to the storage control device from the host processing device, the host processing device designates an actual storage region, which is to be a target of processing, by a logic device which is defined to correspond with the actual storage region, and conducts this processing by a control block (hereinafter referred to as “base control block”) assigned one to one to the logic device.
Here, in a general conventional data processing system, only one base control block could be assigned to the I/O processing of the certain logic device. Thus, for example, when the I/O request continuously occurs in respect to the certain logic device, a processing of the next I/O request could not be conducted until the processing of the previous I/O processing was completed, thereby causing a waiting time at the host processing device to occur.
In order to solve these inconveniences, for example, U.S. Pat. No. 5,530,897 discloses a mechanism where, in a case a base control block (in the above document, “Unit Control Blocks” corresponds to control block) of a certain logic device (hereinafter referred to as “base device”) is in use, the I/O request is processed by a control block (hereinafter referred to as “alias control block”) made to correspond to another logic device (hereinafter referred to as “alias device”) assigned to the logic device.
Incidentally, since the number of alias devices defined between the host processing device and the storage control device is limited, it is ideal for the alias device to be assigned to the base device so the effect of the alias device may be exhibited to a maximum. Therefore, conventionally it was devised to make the effect of the alias device become as large as possible by methods such as in which a user predicts a processing load of each of the base control blocks and fixedly assigns the alias devices (i.e., static method) or in which the host processing device automatically assigns the alias devices according to the processing load of the base control block (i.e., dynamic method).
However, the assignment of the alias control blocks by the static method or the dynamic method is based on mainly circumstances of the host processing device such as a load state of the base control block, so that from the point of view of process efficiency of the entire data processing system comprised of the host processing device and the storage control device, there are many cases where assignment of the alias control block is not always optimized. For example, even if many alias devices are assigned to a base device with a high processing load, and waiting at the host processing device is decreased, if the I/O processing load in respect to a physical device of the storage control device is large, the effect of the alias control block from the viewpoint of the entire data processing system will be reduced.